All classrooms at Camberley School will be back in use today after a chemical spill forced the school to close on Monday.

An old fashioned mercury thermometer broke in the science area on Friday afternoon and even though the broken parts were picked up the mercury vaporised during the weekend in the 30C heat.

The school was open for students again yesterday but the two affected classes were housed in spare classrooms despite receiving clear readings from an air assessment done by the Fire Service.

Camberley School principal Tamla Smith said they were satisfied that all classrooms were ready for use again today.

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She said the quick action from the staff and agencies meant the risk to everyone's health was vastly reduced.

"As soon as the teacher suspected a funny smell we got the students out and put them in the hall so no one was exposed to the toxic smell all day."

The school was evacuated within about an hour and 13 students, two teachers and a parent were taken to Hawke's Bay Hospital as a precaution.

Ms Smith said they were all discharged on Monday night.

Liquid mercury is not readily absorbed through skin but vaporises at room temperature and inhaling the vapour can be harmful.

Symptoms of exposure to the neurotoxin include tremors, insomnia, neuromuscular changes and headaches.

Fire crews and a hazardous materials team decontaminated the affected area on Monday afternoon ventilating the affected classroom and removing the carpet.